Different effects of startling acoustic stimuli (SAS) on TMS-induced responses at rest and during sustained voluntary contraction

Previous studies have shown that a habituated startling acoustic stimulus (sas) can cause a transient suppression of motor evoked potentials (meps) induced by transcranial magnetic stimulation (tms) during light muscle contraction. however,it is still unknown whether this phenomenon persists when at rest or during a sustained voluntary contraction task. therefore,the purpose of this study was to determine whether a conditioning sas has different effects. tms was delivered to the hot spot for the left biceps on 11 subjects at rest both with and without a conditioning sas. of the 11subjects,9 also had tms delivered during isometric flexion of the left elbow,also with and without a conditioning sas. tms-induced meps,tms-induced force,and silent periods were used to determine the effect of conditioning sas. consistent with previous findings,tms-induced meps were smaller with a conditioning sas (0.49 ± 0.37 mv) as compared without the sas (0.69 ± 0.52 mv) at rest. however,a conditioning sas during the voluntary contraction tasks resulted in a significant shortening of the mep silent period (187.22 ± 22.99 ms with sas vs. 200.56 ± 29.71 ms without sas) without any changes in the amplitude of the mep (1.37 ± 0.9 mv with sas v.s. 1.32 ± 0.92 mv without sas) or the tms-induced force (3.11 ± 2.03 n-m with sas v.s. 3.62 ± 1.33 n-m without sas). our results provide novel evidence that a conditioning sas has different effects on the excitability of the motor cortex when at rest or during sustained voluntary contractions. © 2016 chen,li,zhou and li.